Lt. Greg Raelson, a spokesman for the Navy's Bahrain-based 5th Fleet, gave no immediate word on the fate of the crew. But an Omani air force official said three of them have been found so far and are being treated in a hospital.
The Omani official was not authorized to release the information and spoke on condition of anonymity.
No hostile activity was suspected.
Raelson said an investigation is under way into crash of the MH-53E Sea Dragon. He said the helicopter was involved in heavy lift operations when it crashed on land some 58 miles southwest of the capital Muscat.
A similar helicopter from the same squadron was on the scene carrying out search and rescue operations.
The downed chopper is assigned to Helicopter Mine Countermeasure Squadron 15, which is based in Norfolk, Va. The duty officer at the squadron base in Virginia said he didn't have any further details to report.
The three-engine MH-53E is able to operate from aircraft carriers and other warships, and is mainly used for minesweeping operations.
Oman lies on the southeastern corner of the Arabian Peninsula. Along with Iran, it controls access to the Strait of Hormuz, a narrow waterway at the mouth of the Gulf that is the route for a fifth of the world's oil supply.
The sultanate maintains close diplomatic ties with both Washington and Tehran.
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